Fire retardant cellulosic materials

ABSTRACT

Cellulosic materials such as wood chips, textile fibers and the like are treated to produce products such as particle board having enhanced fire and heat resistant properties. For example, wood chips are saturated with an eqimolar aqueous solution of monoammonium phosphate and diammonium phosphate. A metal hydroxide is added to the solution. The saturated wood chips are dried and mixed with a modified glue composition. The glue that which contains urea formaldehyde and/or phenolic resin is in powdered or brown marble form and dissolved in water. The treated wood chips and modified glue is then mixed, formed into a mat and placed under pressure at about 120° C. for 8 to 15 minutes. The pressure may range from about 300 to 400 psi.

FIELD OF THE INVENTION

[0001] This invention relates to a fire retardant cellulosic materialand more particularly to a fire retardant particle board having improvedflame and heat resistance.

BACKGROUND FOR THE INVENTION

[0002] Cellulosic materials such as paper, wood, cotton and the like arecommonly used for household and commercial applications. Such materialsare highly flammable and when ignited the fire spreads rapidly.Nevertheless, such materials are commonly used. Accordingly, a number ofmethods for treating such materials to reduce their flammability havebeen developed. However, such methods may be inadequate for today'sstandards, may prove too costly for the commercial market, provide toolittle protection against fire and smoke and result in products withother shortcomings.

[0003] The use of cellulosic products which are treated with fireretardant materials frequently involve human beings, who incorporatesuch products in a confined space as for example in a home, kitchen orother room. Therefore the products must provide a safe environment andat the same time provide a pleasing appearance particularly when theproducts are made of particle board. Therefore the use of volatile orharmful solvents should be minimized and preferably avoided.

[0004] It is also important to eliminate volatile or harmful solventswhich could cause problems during a process for treating cellulosicmaterial with a flame retardant agent. Further, it is important that anytreatment minimizes the likelihood of chemical exuding from theprocessed material. It is also important that any chemical treatmentshould not produce or release toxic substances onto the surface of aproduct.

[0005] Conventional methods for treating cellulosic materials such asparticle board and the like typically include the application of saltsof phosphoric acid, boric acid etc. Other methods use various organicsolvent systems. Both of such methods may be economical, but oftenresult in crystallization of salts on the surface of a wood product. Inaddition, such methods may result in migration of undesirable chemicalsto the surface of products made thereby. The solvents used are oftenvolatile during the application of the flame retardants and exude fromthe finished products.

[0006] It has also been recognized that ammonium phosphates are amongthe more effective inorganic fire retardants which are commonly used totreat cellulosic materials. Such phosphates are typically present asdiammonium phosphate, monoammonium phosphate or simple or complexmixtures of such phosphates. Fire retardants of this type are preparedby reacting aqueous phosphorous acid with an alkaline oxide such asethylene oxide.

[0007] A more recent approach to provide a non-blooming fire retardantcomposition is disclosed in the U.S. Pat. No. 4,539,045 of Wagner. Asdisclosed therein, an ammonium phosphate-containing fire retardantincludes an effective amount of boric acid or alkali metal borate. Theammonium phosphate-containing fire retardant comprises a reactionmixture of aqueous phosphoric acid and an alkylene oxide. Boric acid oralkali metal borate is present in an amount of from about 2.5 to about12 percent by weight of solids.

[0008] It is now believed that there may be a large commercial demandfor an improved fire retardant cellulosic products in accordance withthe present invention. It is believed that this demand extends to a fireretardant particle board which has improved heat and flame resistance. Ademand for an improved fire retardant cellulosic material is furthersupported by the products' enhanced properties. For example, suchproducts do not include toxic substances and produce minimal smoke whenexposed to heat and/or open flame. Accordingly, there is no harmfulvapor or toxic substance to deal with during the manufacturing process.

[0009] In addition, products in accordance with the present invention donot exude toxic substances during or after manufacture or when exposedto high temperatures and/or open flame. Further the chemicalsincorporated do not migrate to the surfaces or result in unsightlyblemishes. Finally it is believed that the products as disclosed hereincan be manufactured in a cost effective manner and brought to market ata competitive price.

BRIEF SUMMARY OF THE INVENTION

[0010] In essence, the present invention contemplates a fire retardantcellulosic material and more particularly a fire retardant particleboard which is made from wood chips and/or fibers. The particle boardcomprises from about 60 to about 75 percent by weight cellulosicmaterial, preferably in the form of wood chips. Such chips have the samemix of particle sizes which are incorporated in the manufacture ofconventional particle boards and may be in the form of wood fibers orfiber like chips. The particle board also includes from about 8 to about12 percent by weight of a glue which is selected from the groupconsisting of urea formaldehyde resin, phenolic resin and mixturesthereof as well as other conventional industrial glues. In addition tothe above, the particle board includes between about 6.6 and 13.6percent by weight monoammonium phosphate and between about 7.4 and about15.6 percent by weight diammonium phosphate. An important aspect of theinvention resides in using about equal or preferably equal molarconcentrations of the monoammonium phosphate and the diammoniumphosphate. In addition, the particle board includes about 0.8 and about1.6 percent by weight metal hydroxide and preferably aluminum hydroxide.

[0011] In a preferred embodiment of the invention the particle boardcontains between 67 and 74 percent by weight wood chips and between 10and 12 weight percent of a treated urea formaldehyde resin. It alsocontains from 6.5 to 10 percent by weight monoammonium phosphate andfrom 7.4 to 11.2 percent by weight diammonium phosphate. In addition,the particle board includes between 0.8 and 1.15 percent by weightaluminum hydroxide.

[0012] The particle board is produced in accordance with a method asdisclosed and claimed in my copending application entitled, “A MethodFor Producing A Flame Retardant Cellulosic Sheet Material,” which wasfiled on even date herewith. That method incorporates an aqueoussolution which is disclosed and claimed in my copending applicationentitled, “Fire Retardant Composition,” which was filed on the same dateas this application. That method also incorporates an improved ortreated urea formaldehyde resin as disclosed in my copending applicationentitled, “A Flame Retardant Glue And Method For Making The Same,” whichwas also filed on the same date as the present application. All of mycopending applications mentioned above are incorporated herein in theirentireties by reference.

[0013] The invention will now be described in connection with theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a graphical representation showing the composition of afire retardant composition or solution as used in the production offlame retardant particle boards in accordance with the presentinvention;

[0015]FIG. 2 is a pie chart illustrating the compositions of onepreferred solution from FIG. 3;

[0016]FIG. 3 is a pie chart illustrating a preferred glue composition asused in the production of a fire retardant particle board in accordancewith the present invention;

[0017]FIG. 4a, b, c are flowcharts illustrating the process steps forimparting improved flame and/or fire retardancy to particle board or thelike in accordance with the present invention;

[0018]FIG. 5 is graphical representation of the final composition of afire retardant particle board which was made in accordance with thepresent invention and shows the composition in weight percent at variousmolar concentrations of monoammonium phosphate and diammonium phosphate;and

[0019]FIG. 6 is a pie chart illustrating the preferred composition of afire retardant particle board from FIG. 1 at 0.4M MAP/DAP.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0020] The widespread use of cellulosic particle board and increasedconcern for safety has led to a demand for an improved flame retardantfiber board. For the purpose of the present invention, the termcellulosic particle board encompasses boards such as hard boards,particle board, fiber board, medium density fiber board (MDF), orientedstrand board, card board and other pulp products which are made ofcellulosic material. Such boards are made from cellulosic materialsselected from a group consisting of wood fibers, sawdust, wood particlesor chips, bagasse and cellulosic fibers to include pulp, pulp extractsand paper of all grades.

[0021] As contemplated by the present invention, wood chips or fibers ofthe type used in manufacturing conventional fiber board may be used inproducing an improved particle board as disclosed herein.

[0022] The first step in manufacturing a cellulosic particle board withenhanced flame and heat retarding characteristics requires the use of afire retardant solution as defined hereinafter.

Fire Retardant Solutions

[0023] In general the fire retardant composition or solution asdisclosed herein comprises an aqueous solution for use in impregnatingcellulosic materials and textile fibers. The solution containsmonoammonium phosphate and diammonium phosphate in equal molar amounts.For example the molar amounts of monoammonium phosphate and diammoniumphosphate range from about 0.3 moles per liter to about 0.95 moles perliter or until maximum dissolution of both chemicals and preferablybetween about 0.35 moles per liter and 0.55 moles per liter. A metalhydroxide, aluminum, calcium or magnesium and preferably an aluminumhydroxide is added to the solution in an amount of between about 3.75and about 11.87 grams per liter.

[0024] In the preferred solutions, the molar concentrations of themonoammonium phosphate (MAP) and diammonium phosphate (DAP) are equaland within the range of 0.35 and 0.55 moles per liter. Examples ofcompositions for use in the manufacture of cellulosic particle board andtreatment of textile fibers are given in the following table. Inaddition to the examples shown, tests were conducted on samplecompositions wherein the aluminum hydroxide was replaced with an equalamount of calcium hydroxide and also with an equal amount of magnesiumhydroxide. Tests on those compositions were comparable to those obtainedwith aluminum hydroxide. TABLE 1 Moles MAP in Grams DAP in Grams Al (OH)3 0.3 34.5 39.6 3.75 0.35 40.25 46.2 4.375 0.4 46 52.8 5 0.45 51.75 59.45.625 0.5 57.5 66 6.25 0.55 63.25 72.6 6.875 0.6 69 79.2 7.5 0.65 74.7585.8 8.125 0.7 80.5 92.4 8.75 0.75 86.25 99 9.375 0.8 92 105.6 10 0.8597.75 112.2 10.625 0.9 103.5 118.8 11.25 0.95 109.25 125.4 11.875

[0025] The various compositions are also shown in FIG. 1 wherein theconcentration of diammonium phosphate and monoammonium phosphate inpercent by weight versus molar concentrations are shown. The curve 2shows the content of the diammonium phosphate in percent by weight whilethe curve 4 shows the content of the monoammonium phosphate. A curve 6illustrates the content of aluminum hydroxide which is added to thesolution.

[0026] A representative example of a solution is shown in FIG. 2 by apie chart which illustrates the percent by weight of each of theingredients. For example the solution shown in FIG. 2 contains about 91percent water as indicated by 5, five percent diammonium phosphate 6,four percent monoammonium phosphate 7 and less than one percent aluminumhydroxide as indicated by the numeral 8. A process for making thesolution of Table 1 will be described hereinafter in connection withFIG. 4a.

[0027] In the manufacture of a particle board as disclosed herein, oneliter of one of the above-identified solutions is added to about 500grams of dry wood chips. The dry wood chips should have a moisturecontent of about 15 percent of less. The mixture of the wood chips andsolution is thoroughly mixed until the wood is completely saturated. Forexample, the mixture may be stirred with a conventional mixer with shaftor rotating mixer with shaft of the type used with a five-galloncontainer at medium speed. The mixture is stirred for about 10 to 15minutes and until the mix reaches a uniform dark brown color. Thestirring may be continued for about one minute after displaying theuniform dark color to assure complete saturation.

[0028] The saturated wood chips are then dried to a uniform light brownor tan color at a temperature of between about 100 to 120° C. for about45 minutes to about 70 minutes with some stirring. At this stage thewood chips will have a moisture content of about 15 percent. Thesetreated wood chips or dried saturated wood chips are then mixed with amodified glue composition as will be described below.

Modified Glue Composition

[0029] The fire retardant cellulosic materials disclosed herein alsoinclude a modified glue composition. That composition is made from aurea formaldehyde resin, phenolic resin or mixtures thereof in the formof a dry powder. Preferred glues include conventional particle boardglues such as Kaltliem Type h and Kaurit. In preparing a modified gluecomposition, about 75 grams of a urea formaldehyde powdered glue areadded to about 100 milliliters of water and thoroughly mixed or stirredat about 30-50° C. If a phenolic resin is used the glue water MAP/DAPsolution is mixed at about 60° C. The glue, which may be in a brownmarble form, is mixed or stirred until all of the glue is dissolved toform an emulsion. Then, about 4 grams of monoammonium phosphate andabout 4 grams of diammonium phosphate are dissolved in about 25milliliters of water in a separate beaker. An additional one gram ofaluminum hydroxide may also be added. This ensures that essentially allof the MAP/DAP dissolves in the water. The metal hydroxide may dissolveslightly but most will be undissolved but suspended in the glue watersolution.

[0030] All of the glue water solution is mixed with about 25 millilitersof the water, monoammonium phosphate, diammonium phosphate mix tothereby form the modified glue composition. The monoammonium phosphateand diammonium phosphate are present in about equal if not equal molarconcentrations.

[0031] In a second example of a modified glue composition, about 68grams of powdered glue is dissolved in about 100 milliliters of water.Then between about 3.6 to about 4.4 grams of monoammonium phosphate andabout 3.6 to about 4.4 grams of diammonium phosphate is mixed in aseparate beaker with about 25 milliters of water to thereby form amodified glue composition by mixing both solutions in the manner shownin the flow chart FIG. 4b.

[0032] One preferred glue composition is illustrated in FIG. 3. As showntherein, the glue composition includes about 60 percent by weight wateras indicated by the wedge 10, about 36 percent by weight areaformaldehyde resin 12, about 2 percent by weight monoammonium phosphate14 and about 2 percent by weight diammonium phosphate. As indicated theglue composition contains between about 0%-10% by weight aluminumhydroxide 16. In some compositions this aluminum hydroxide is totallyeliminated.

[0033] In a further example of a modified glue composition, about 82grams of powdered glue is dissolved in about 100 milliliters of water.This initial solution is then mixed with a monoammonium phosphate,diammonium phosphate solution in the same manner and amounts as setforth in the aforementioned second example.

[0034] A number of other glue compositions were made using phenolformaldehyde. Each of those compositions were made by warming about 200milliters of water to about 60° C. Then about 40, 60, 80, 100 and 120grams of the powdered glue were each dissolved in about 200 milliters ofwarmed water with mixing. In a separate beaker about 6 grams ofmonoammonium phosphate and about 6 grams of diammonium phosphate weredissolved in water and the resulting solution added to each of thepowdered glue water solutions mentioned above. Additional experimentswere conducted using increments of 8, 10, 12, 14 and 16 grams each ofmonoammonium phosphate and diammonium phosphate. Each of the treated ormodified glues had improved flame retardant properties.

Method For Making Fire Retardant Materials

[0035] A method for making cellulosic sheet material, as for exampleparticle board, with enhance resistance to fire, flame and heat will bedescribed in connection with FIGS. 4a-4 c. As illustrated in FIG. 4c,the method includes the step 20 of providing a mass of wood chips orfibers having a moisture content of 15 percent or less. The particlesize of the wood chips may vary widely, but are preferably in the samerange of particle sizes as used in manufacturing conventional particleboard. Separation of small particles from larger ones may be done tomake a conventional sandwich particle board.

[0036] The method also includes the step 22 of providing an aqueoussolution of monoammonium phosphate (MAP) and diammonium phosphate (DAP)wherein the MAP and DAP are present in equal molar lower concentrationsas for example from FIG. 4a. Such solutions which include a small amountof aluminum hydroxide are described above in the section of thisspecification identified as Fire Retardant Solutions. For example, aboutone liter of one of these solutions of Table 1 is added to between about450 to 550 grams and preferably about 500 grams of dried wood chips instep 24.

[0037] In step 26, the wood chips are saturated with the solution fromstep 22. This saturation is accomplished by mixing or stirring the woodchips and solution for about 10 to 15 minutes at a temperature withinthe range of about 20 to 25° C. When the wood chips are thoroughlysaturated, the mix will take on a uniform dark brown color. This colorchange is relatively slow and usually takes place over a period of aboutseveral minutes, i.e. after mixing for approximately 10-20 minutesdepending on the mixer efficiency.

[0038] The saturated wood chips from step 26 are then dried in aconventional manner in step 28. This drying will normally be conductedat a temperature slightly higher than 100° C. (105°-110°) using care toensure that only the water evaporates. The drying is continued until thedried saturated wood chips have a moisture content of about 15 percentor less. The drying step was accomplished in about 40-75 minutesdepending on the relative humidity from temperature. At this point, thetreated wood chips referred to herein from time to time as driedsaturated cellulosic material will have a light tan color. Drying canalso be done using a microwave oven set at low to medium power or byother conventional means. Using a microwave oven requires opening theoven and stirring every 2 to 3 minutes.

[0039] The method disclosed herein also includes a step 30 of providinga modified glue composition as described above in the section identifiedas Modified Glue Composition, continued from FIG. 4b. In that step aurea formaldehyde powdered glue such as one available from BASF andidentified as Kaltliem Type H is dissolved in water. This treated ormodified glue composition contains between about 54 to about 66 percentby weight water, between about 33 to about 39 percent by weight glue andbetween about 1.5 and about 2.5 weight percent MAP and about the sameamount of DAP. A small amount of aluminum hydroxide, about one percentor more by weight may be added.

[0040] In step 32 the modified glue composition is mixed with about 500grams of the dried saturated wood chips, i.e. the wood chips that weresaturated with the solution in step 26 and dried in step 28. This massof wood chips and modified glue form a mass or mat of treated woodchips. This mass or mat is then place on a conventional platen andsubjected to heat and pressure in the same manner, temperature andpressures as used in manufacturing conventional particle board. Forexample the mat of particles may be subjected to a pressure of about 350to 400 psi at a temperature of about 110-195° C. and preferably above120° C.

[0041] At times a finished particle board made in accordance with themethods disclosed herein may have a thin white film on the surface ofthe board. This film may be readily removed by wiping with a damp cloththat is either slightly basic or slightly acidic as for example withsodium or potassium hydroxide or hydrochloric or sulfuric acid,respectively.

[0042] It is also contemplated that a thin laminate as for example witha surface finish such as wood grain may also be added to the particleboard in accordance with the present invention. In such application thelaminate is dipped in a solution as disclosed herein, dried and glued tothe surface of the particle board with a treated glue composition asdisclosed herein.

Particle Board Composition

[0043] The cellulosic sheet material or particle board composition asdisclosed herein contains between about 60 to about 75 percent by weightwood chips, from about 8 to about 12 percent by weight of a modifiedglue as described above, between about 6.6 to about 13.6 percent byweight monoammonium phosphate and between about 7.4 and about 15.6percent by weight diammonium phosphate. The particle board also containsbetween 0.8 and 1.6 percent by weight aluminum, calcium or magnesiumhydroxide. In the composition disclosed herein, the molar concentrationof the monoammonium phosphate and diammonium phosphate are about equaland preferably equal. Examples of particle board compositions havingenhanced resistance to fire, flame and heat are given in the followingTable 2. TABLE 2 % MAP % DAP % Al % Wood Chips 5.817028 6.5875950.717685 75.54581854 6.557256 7.438966 0.796503 74.09328344 7.2695558.258215 0.872347 72.69555103 7.955478 9.047126 0.945382 71.349577258.616462 9.807356 1.015762 70.0525394 9.253844 10.54044 1.08362968.80181637 9.868866 11.2478 1.149115 67.59497093 10.46268 11.930781.212343 66.42973395 11.03637 12.59061 1.273428 65.30399007 11.5909513.22845 1.332477 64.21576497 12.12734 13.84538 1.389591 63.1632137412.64643 14.44241 1.444862 62.14461051 13.14904 15.02049 1.49837961.15833894 13.63595 15.58051 1.550224 60.20288372

[0044] The composition of the particle boards in accordance with thepreferred embodiments of the invention are illustrated by FIG. 5. Asshown therein, the curve 22 indicates the percent by weight wood chipswhile the curve 24 indicates the percent by weight glue. The weightpercent of DAP and MAP are illustrated by the curve 26 and 28respectively. Finally, the curve 30 illustrates the percent by weightaluminum hydroxide.

[0045] One preferred embodiment of the invention is illustrated by a piechart in FIG. 6. As indicated therein the particle board contains about73 percent by weight wood is shown by the wedge 32 and about 11 percentby weight includes powdered glue as indicated by the numbers 34. About 8percent by weight DAP and 7 percent by weight MAP are indicated by thesegments 36 and 38 respectively. Finally the numeral 40 shows that 1percent by weight aluminum hydroxide in the final composition.

[0046] While the invention has been described in connection with itspreferred embodiments, it should be recognized that changes andmodifications may be made therein without departing from the scope ofthe appended claims.

What is claimed is:
 1. A fire retardant particle board comprising fromabout 60 to about 75 percent by weight cellulosic material, from about 8to about 12 percent by weight glue selected from the group consisting ofphenolic resin and urea formaldehyde resin and mixtures thereof, betweenabout 6.6 and about 13.6 percent by weight monoammonium phosphate,between about 7.4 and about 15.6 percent by weight diammonium phosphateand between about 0.8 and about 1.6 percent by weight metal hydroxideand wherein the molar concentration of said monoammonium phosphate andsaid diammonium phosphate are about equal.
 2. A fire retardant particleboard according to claim 1, in which said glue is a powdered ureaformaldehyde resin.
 3. A fire retardant particle board according toclaim 2, in which said particle board comprises a mass of wood fibers.4. A fire retardant particle board according to claim 2, in which saidcellulosic material comprises a mass of wood chips.
 5. A fire retardantparticle board according to claim 4, which includes from about 67 toabout 74 percent by weight wood chips, between about 10 to about 12percent by weight urea formaldehyde resin, from about 6.5 to about 10percent by weight monoammonium phosphate and from about 7.5 to about11.2 percent by weight diammonium phosphate and between about 0.8 andabout 1.15 percent by weight aluminum hydroxide.
 6. A fire retardantparticle board according to claim 5, which includes about 73 percent byweight wood chips, about 10.5 percent by weight urea formaldehyde glue,about 7.3 percent by weight monoammonium phosphate, about 8.3 percent byweight diammonium phosphate and about 0.9 percent by weight aluminumhydroxide.
 7. A fire retardant particle board according to claim 5,which includes about 71 percent by weight wood chips, about 10 percentby weight urea formaldehyde glue, about 8 percent by weight monoammoniumphosphate and about 9 percent by weight diammonium phosphate.
 8. A fireretardant particle board according to claim 5, which includes about 70percent by weight wood chips, about 10 percent by weight ureaformaldehyde resin, about 9 percent by weight monoammonium phosphate,about 10 percent by weight diammonium phosphate and about 1.0 percent byweight aluminum hydroxide.
 9. A fire retardant particle board accordingto claim 5, which includes about 69 percent by weight wood chips, about10 percent by weight urea formaldehyde glue, about 9 percent by weightmonoammonium phosphate, about 11 percent by weight diammonium phosphateand about 1 percent by weight aluminum hydroxide.
 10. A fire retardantparticle board according to claim 5, which includes about 68 percent byweight wood chips, about 8.9 percent by weight urea formaldehyde resin,about 10 percent by weight monoammonium phosphate, about 11 percent byweight diammonium phosphate and about 1.1 percent by weight aluminumhydroxide.
 11. A fire retardant particle board according to claim 1 inwhich said glue is phenol formaldehyde.